Sensor size is made more confusing by the archaic way that they are described. Think of the fractions as if there were no decimals involved. 1/1 is bigger than 1/2. 1/1.7″ is bigger than 1/2.5″. As a general guideline, the bigger the sensor, the better the image quality.

1/2.5″ is probably the most common sensor size in point and shoot digital cameras. It is about 5 mm by 4 mm, or 20 square millimeters.

1/1.8 is 7.2 mm by 5.3 mm or about 38 square millimeters.

I don’t know the exact dimensions of 1/1.7″, but it would be slightly larger than the 1/1.8″, although mot so much larger that it would offer any real advantage in image quality.

Here’s a good page to study:

One question that we get fairly often here is, “How do I make my subject in sharp focus with a blurry background?” The smaller the sensor, the harder it is to accomplish this. You will see an explanation (if you want details) on this page:

Another thing that you might notice is that the “super zoom” point and shoot cameras tend to have the 1/2.5″ sensor. Since focal length is a function of image size, this is how the camera designed is able to achieve such extreme zoom power (10x – 12x is common). The smaller the sensor, the greater the “lens factor.” A Canon Powershot S3-IS is said to have an “equivalent focal length” of 36 mm-to-432 mm. Considering the lens factor of 6.03x for all 1/2.5″ sensors, the real focal length of this lens is about 6 mm-to-72 mm.

Here is a mini-tutorial I made myself to compare 10 MP sensors in a digital SLR (DSLR) and a point and shoot (P&S) camera. I have tried to keep everything on equal footing with no unequal cropping of the original images. Both images were taken at the equivalent of 75 mm from about 1,000 feet away. View this FULL SIZE and scroll through the image to compare the resolution at various points of the images. To me, the P&S sensor practically looks like an impressionist painting compared to the DSLR sensor. Please note also that this is the “large size” P&S sensor, as most are using the smaller 1/2.5″ (5×4 mm) sensor.

Here is a comparison between 10 MP image from the SD900, which is a 1/1.8″ sensor, and a 6 MP image from an SD700-IS, which is a 1/2.5″ sensor. Okay, I don’t know if we are comparing pixel count or sensor size here, but take a look anyway and see what you think about the differences. This MIGHT be somewhat analogous to comparing the Sony W200 vs. W90, but not for the W100 vs. W90, as those two have the same pixel count.

Your Sony uses a proprietary card, so sticking with Sony is the thing to do.

Sensor wise, I have placed a link below that will explain all those goofy 1/1.7″, 1/2.5″ ramblings (BTW the 1/1.7″ is the larger sensor … go figure).

I think it is the image stabilization why you would pay the extra money for a smaller sensor